Explanation:
An alluring Comet Hartley 2
cruised through
planet Earth's night sky on October 8,
passing within about a Full Moon's
width of the famous double star cluster in Perseus.
The much anticipated
celestial photo-op
was recorded here
in a 3 frame mosaic with greenish comet and the
clusters h and Chi Persei
placed at the left.
The well-chosen, wide field of view spans about 7 degrees.
It extends across the constellation boundary into Cassiopeia,
all the way to the Heart Nebula (IC 1805)
at the far right.
To capture the cosmic moment, a relatively short 5 minute exposure
was used to freeze the moving comet in place, but
a longer exposure with a narrow-band filter was included in the
central and right hand frames.
The narrow-band exposure brings out the fainter
reddish glow
of the nebula's atomic hydrogen gas, in contrast
to the cometary coma's
kryptonite green.
In the past few days,
comet watchers have reported that Hartley 2
has become just visible to the unaided eye for experienced observers
from dark, clear sites.
On October 20, the
comet will
make its closest approach to Earth,
passing within about 17 million kilometers.
On November 4, a
NASA spacecraft will fly by the
comet's small nucleus
estimated to be only 1.5 kilometers in diameter.